I. Field of the Invention
The present invention relates generally to fluid filtering devices and, more particularly, to such a device adapted for connection to the return line of a hydraulic system.
II. Description of the Prior Art
Hydraulic fluid systems conventionally include a reservoir of hydraulic fluid, a suction line for fluidly connecting the reservoir to the hydraulic pump, and a fluid return line from the hydraulic system to the reservoir. The hydraulic fluid within the hydraulic system becomes contaminated during operation of the system and these contaminants must be filtered from the hydraulic fluid in order to prevent damage to the hydraulic pump and other components within the hydraulic system. There have been a number of previously known fluid filtering devices which are fluidly connected to either the suction line from the reservoir or the return line to the reservoir.
There have been a number of previously known return line filters which include a tubular cylindrical housing having one end positioned within the fluid reservoir and into which a filter assembly is slidably received. The filter assembly typically includes an extension tube coaxially secured to a tubular filter element so that upon insertion of the filter assembly into the housing, the filter element is spaced radially inwardly from the interior walls of the housing. In addition, suitable fluids seals are provided at each axial end of the filter element for fluidly sealing the filter element to the housing.
In operation, the return fluid from the hydraulic system first enters the annular chamber between the filter element and the housing, passes through the filter element and finally exits through the lower open end of the filter element and to the fluid reservoir. This type of previously known return line filter is particularly advantageous in that the filter assembly can be removed from the housing without interruption of fluid flow through the hydraulic system return line.
One disadvantage of this type of previously known return line filter is that since the annular or inlet chamber between the filter element in the housing is pressurized, a certain amount of leakage past the fluid seals at both axial ends of the filter element inherently occurs. Fluid leakage past the seals at the lower axial end of the filter element creates no adverse effect since the leakage is merely returned to the fluid reservoir. Conversely, leakage past the seals of the upper end of the filter element accumulates in the interior of the housing above the filter element and within the interior of the extension tube. Thus, when the filter assembly is removed from the housing, this leakage fluid is drawn out with the filter assembly and spills on the workmen and on the floor surrounding the fluid reservoir. Since oil is conventionally used as the hydraulic fluid, the spillage of the oil on the floor creates a serious safety hazard for workmen engaged around the fluid reservoir.